If you graft an immature citrus twig onto a mature root stock, the young citrus will not produce fruit until it reaches it predetermined node count required for maturity. This could be either a shorter time, or a longer time depending on what node count number the grafted twig had reached when it was cut from the mother tree. Citrus when removed from a tree, and then grafted onto a rootstock "remembers" what node count it had achieved before it was removed, and starts growing from that point.
I only agree to some points. As I observed, some new young branches, in a matured tree, started to flower right away in the spring. I assume if I cut a 2 months old branches from a matures tree and grafted to another matured rootstock, then it might fruit right away in the same year or next year. I have not tried on citrus but in jujube I did. I grafted young 6 months old jujube branches onto a 7 years old rootstock in early spring, and it started to flower and fruit right a away after 2 months.
I also grafted other jujube branches onto small jujube rootsuckers, and it did not flower at all until several years later. I guess your opinion might make some sense in citrus, but let see. I need more time to do experiment on citrus.
In my experience, rootstock vigor and age played a vital role (at least 70%) in maturing speed of the grafted scionwood. The matured and vigours rootstock did boost the rate of maturation of the grafted scionwood and on the other hand, the immatured and less vigorous rootstock will for sure delay the maturing speed of the scionwood. I also have done grafting a matured scionwood jujube on a small young rootstock and it delayed on flowering and fruiting.
Don't trust 100% any document online unless we verify that ourself. Many research publication has been published and then years later contradicting that by a new publication.